DENVER -- Apple Computer came under fire for back-pedaling on its support for IPv6, the next-generation Internet Protocol, at a gathering of experts held in Denver this week.

Presenters at the North American IPv6 Summit expressed annoyance that the latest version of Apple's AirPort Utility, Version 6.0, is no longer compatible with IPv6. The previous Version, 5.6, offered IPv6 service by default.

Comcast, for example, is urging its subscribers that are interested in using IPv6 not to upgrade to AirPort Utility Version 6.0 if they use the OS X Lion operating system because of incompatibilities with IPv6.

"Apple has taken the ability to seamlessly support IPv6 away from the AirPort Utility," said John Brzozowski, chief architect for IPv6 and distinguished engineer with Comcast. "It's a little concerning. We hoped to see more IPv6 support, not less, among [customer premises equipment] vendors."

Apple's AirPort Utility 6.0, released in January, allows users to set-up and manage Wi-Fi networks. Because Version 6.0 of AirPort Utility doesn't support IPv6, users also must install the older version 5.6 in order to run IPv6.

Indeed, Comcast is giving only a conditional recommendation for Apple's AirPort Utility to be used along with its new home networking service for IPv6. In contrast, Comcast offers a blanket recommendation for various IPv6-enabled home gateway models from D-Link, Cisco and Netgear.

Comcast is the first U.S. ISP to offer an IPv6 service for home gateway users, which will be officially announced later this month. Currently, Comcast is offering this service in two U.S. cities. The service allows Comcast residential subscribers with IPv6-enabled home gateways to have native IPv6 support on any device connected to the Internet.

Overall, home networking products like AirPort Utility have been slow to adopt IPv6.

"Home gateways have been one of the areas that was slowing IPv6 adoption," said Timothy Winters, senior manager at the University of New Hampshire's Interoperability Lab. The lab is running a major interoperability test for home gateway equipment next week.

In order to pass the UNH-IOL test, home gateways must enable IPv6 by default and pass a set of interoperability tests. So far, the lab has approved six home gateways as passing 100% of its interoperability tests, including models from Cisco, Actiontec, Broadcom, D-Link and Lantiq. No Apple products are included on the UNH-IOL list.

While home networking vendors like Cisco and D-Link are adding IPv6 across their product lines, Apple appears to be the only vendor that is removing this feature.

Home gateways are a critical class of networking gear that requires upgrading as the Internet migrates from IPv4, the original version of the Internet Protocol, to IPv6.

IPv6 is needed because IPv4 is running out of addresses to connect new users and new devices to the Internet. IPv6 solves this problem with a vastly expanded address space, but it is not backwards-compatible with IPv4. So ISPs like Comcast have to upgrade their routing, edge, security, network management and customer premises equipment to support IPv6. The alternative is for carriers to translate between IPv4 and IPv6 addresses, which adds latency and cost to network operations.